import logging
from datetime import date, datetime
from http import HTTPStatus
from typing import TYPE_CHECKING

from django.conf import settings
from django.utils import timezone

from google.oauth2 import service_account
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError

if TYPE_CHECKING:
    from googleapiclient._apis.calendar.v3 import CalendarResource, Event

from cmsmanage.django_q2_helper import q_task_group
from reservations.models import ExternalReservation, Reservation, Resource

logger = logging.getLogger(__name__)

SCOPES = ["https://www.googleapis.com/auth/calendar"]


def parse_google_calendar_datetime(dt) -> date | datetime:
    if "date" in dt:
        return date.fromisoformat(dt["date"])
    elif "dateTime" in dt:
        return datetime.fromisoformat(dt["dateTime"])
    else:
        raise Exception("Google Calendar event with out a start/end date/dateTime")


class GoogleCalendarSynchronizer:
    service: "CalendarResource"

    def __init__(self) -> None:
        self.service = build(
            "calendar",
            "v3",
            credentials=service_account.Credentials.from_service_account_file(
                settings.GOOGLE_SERVICE_ACCOUNT_FILE,
                scopes=SCOPES,
            ),
        )

    def update_calendar_event(
        self, resource: Resource, existing_event: "Event", reservation: Reservation
    ):
        changes = reservation.make_google_calendar_event()
        # skip update if no changes are needed
        if (
            parse_google_calendar_datetime(existing_event["start"]) != reservation.start
            or parse_google_calendar_datetime(existing_event["end"]) != reservation.end
            or any(
                existing_event[k] != v
                for k, v in changes.items()
                if k not in ("start", "end")
            )
        ):
            logger.debug("Updating event")
            new_event = existing_event | changes
            self.service.events().update(
                calendarId=resource.google_calendar,
                eventId=reservation.google_calendar_event_id,
                body=new_event,
            ).execute()

    def insert_calendar_event(self, resource: Resource, reservation: Reservation):
        new_gcal_event = reservation.make_google_calendar_event()
        created_event = (
            self.service.events()
            .insert(
                calendarId=resource.google_calendar,
                body=new_gcal_event,
            )
            .execute()
        )
        reservation.google_calendar_event_id = created_event["id"]
        reservation.save()

    def insert_or_update_calendar_event(
        self, resource: Resource, reservation: Reservation
    ):
        if not reservation.google_calendar_event_id:
            logger.info(
                "Event in database has no Google Calendar event ID: inserting | %s",
                reservation.google_calendar_event_id,
            )
            self.insert_calendar_event(resource, reservation)

        else:
            # this event was in Google Calendar at some point (possibly for a different
            # resource/calendar), but did not appear in list(). Try to update it, then
            # fall back to insert
            logger.info(
                "Reservation with event id not in Google Calendar: trying update | %s",
                reservation.google_calendar_event_id,
            )
            try:
                event = (
                    self.service.events()
                    .get(
                        calendarId=resource.google_calendar,
                        eventId=reservation.google_calendar_event_id,
                    )
                    .execute()
                )
                self.update_calendar_event(resource, event, reservation)
            except HttpError as error:
                if error.status_code == HTTPStatus.NOT_FOUND:
                    logger.info(
                        "Event in database not in Google Calendar: inserting | %s",
                        reservation.google_calendar_event_id,
                    )
                    self.insert_calendar_event(resource, reservation)
                else:
                    raise

    def sync_resource_from_google_calendar(
        self, resource: Resource, now: datetime
    ) -> set[str]:
        request = (
            self.service.events()
            .list(
                calendarId=resource.google_calendar,
                timeMin=now.isoformat(timespec="seconds"),
                maxResults=2500,
            )
            .execute()
        )
        if "nextPageToken" in request:
            # TODO: implement pagination
            raise Exception(
                "More events than fit on a page, and pagination not implemented"
            )
        events = request["items"]

        for event in events:
            if (
                "extendedProperties" in event
                and "private" in event["extendedProperties"]
                and event["extendedProperties"]["private"].get("cmsmanage") == "1"
            ):
                try:
                    reservation = resource.reservation_set.get_subclass(
                        google_calendar_event_id=event["id"]
                    )
                    # event exists in both Google Calendar and database, check for update
                    logger.debug(
                        "Event in Google Calendar found in database: checking for update | %s",
                        event["id"],
                    )
                    self.update_calendar_event(resource, event, reservation)
                except Reservation.DoesNotExist:
                    # reservation deleted in database, so remove from Google Calendar
                    logger.info(
                        "Event in Google Calendar not found in database: deleting | %s",
                        event["id"],
                    )
                    self.service.events().delete(
                        calendarId=resource.google_calendar,
                        eventId=event["id"],
                        sendUpdates="none",
                    ).execute()
            else:
                logger.debug(
                    "Event in Google Calendar not originated by CMSManage: adding/updating as external reservation | %s",
                    event["id"],
                )
                # TODO: this might cause issues if something external
                # creates events with matching IDs in different calendars
                reservation, created = ExternalReservation.objects.update_or_create(
                    google_calendar_event_id=event["id"],
                    defaults={
                        "title": event["summary"],
                        "start": parse_google_calendar_datetime(event["start"]),
                        "end": parse_google_calendar_datetime(event["end"]),
                    },
                )
                reservation.resources.add(resource)

        return {event["id"] for event in events}

    def sync_reservation_from_database(self, reservation: Reservation):
        for resource in reservation.resources.all():
            self.insert_or_update_calendar_event(resource, reservation)

    def sync_resource_from_database(
        self, resource: Resource, now: datetime, existing_event_ids: set[str]
    ):
        reservations = (
            resource.reservation_set.filter(end__gt=now)
            # skip events we already pulled from Google Calendar during this sync
            .exclude(google_calendar_event_id__in=existing_event_ids)
            .select_subclasses()
        )
        # TODO: this could probably be more efficient?
        for reservation in reservations:
            if isinstance(reservation, ExternalReservation):
                logger.info(
                    "External event in database did not exist in future of Google Calendar: deleting locally | %s",
                    reservation.google_calendar_event_id,
                )
                reservation.delete()

            else:
                self.insert_or_update_calendar_event(resource, reservation)

    def sync_resource(self, resource: Resource, now: datetime):
        logger.info(
            "Checking calendar %s for resource %s", resource.google_calendar, resource
        )

        existing_event_ids = self.sync_resource_from_google_calendar(resource, now)
        self.sync_resource_from_database(resource, now, existing_event_ids)


@q_task_group("Sync Reservations with Google Calendar")
def sync_reservations_with_google_calendar():
    synchronizer = GoogleCalendarSynchronizer()
    now = timezone.now()

    for resource in Resource.objects.all():
        synchronizer.sync_resource(resource, now)